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Is It Safe To Use Lithium Batteries In LED Flashlights?

You may have heard that LED flashlights using 18650 lithium batteries run hotter and die sooner. Is there any truth to this?
The short answer: There could be an issue, but likely only with “cheap” LED flashlights—that is, ones that lack circuitry to limit the current flowing through the LED. There should be no problem using lithium batteries in a well-designed LED flashlight that contains current-limiting circuitry inside to protect the LEDs.
We're not talking about rechargeable lithium batteries like those used in notebooks, phones, cameras, tablets, and high-end flashlights. Consumer Reports does not test these individually (although we do test battery life for portable devices and tools that have built-in lithium batteries). We're referring to single-use or primary-cell lithium batteries (actually lithium-iron disulfide, but only industry experts call them that).